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The XMASS 800kgDark Matter Detector
in Kamioka, JapanKai Martens
Kavli-IPMU (WPI)The University of Tokyo
for the XMASS collaboration
@ ICRC 2013, Rio de Janeiro
The XMASS collaboration:Kamioka Observatory, ICRR, Univ. of Tokyo ：
K. Abe, K. Hieda, K. Hiraide, Y. Kishimoto, K. Kobayashi, S. Moriyama, M. Nakahata, N. Oka, H. Ogawa, H. Sekiya, A. Shinozaki, Y. Suzuki, O. Takachio, A. Takeda, D. Umemoto, M. Yamashita, B. Yang Kavli IPMU, University of Tokyo ： J.Liu, K. MartensKobe University: K. Hosokawa, K. Miuchi, A. Murata, Y. Ohnishi, Y. TakeuchiTokai University: F. Kusaba, K. NishijimaGifu University ： S. TasakaYokohama National University ： K. Fujii, I. Murayama, S. NakamuraMiyagi University of Education ： Y. FukudaSTEL, Nagoya University ： Y. Itow, K. Masuda, H. Takiya , H. UchidaSejong University ： N. Y. Kim, Y.D. KimKRISS: Y.H. Kim, M.K. Lee, K. B. Lee, J.S. Lee
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 2
Outline
- experimental program
- current experiment: XMASS 800 kgdesign and calibration
- XMASS 800kg refurbishment
- next step: XMASS 1.5 ton
XMASS results were already presented here at ICRC 2013:session DM-EX01, presentation 131 last Tuesday...
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 3
The XMASS Experiment
Xe detector for weaklyinteracting MASSive particles
Xe -MASS detector Xe MASSive -detector
exploiting Xenon:
- high mass number → SI cross section- no long-lived radioactive isotope- good scintillation yield: ~ 46ph/keV- high density (liquid): 3g/cm3
- 48% odd isotopes (natural) → SD cross section- ββ candidate: 136Xe → 136Ba+2e+2.48MeV
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 4
The XMASS Experimental Program:
100kg reference:arXiv:0912.2405
the PAST:100kg prototype,
(3kg fiducial), 30cmproof of principle
the current incarnation:XMASS 800kg
(100kg fiducial), Ø 80cm
technologyadvantages:
- simple- scalable- self-shielding
24t, + ⊙
(10t fiducial)
Ø 2.5m
the next step:XMASS 1.55 ton total,
1 ton fiducial
future:the ultimate XMASS...
for XMASS resultssee: DM-EX01 131
(was Tuesday...)Y. Suzuki, hep-ph/0008296
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 5
The Kamioka Observatory:
KamLAND (Xe)
CANDLES
NEWAGEEGADS
Super-Kamiokande,(T2K)
XMASS
IPMULab
CLIO Legend:DM, , , GW
3km
to M
ozum
i
new: KAGRA
Tokyo
Nagoya
IPMU Lab:U, Th → HP-Ge ← few 100ppt
→ ICP-MS ← 1ppq*Kr → API-MS ← 1ppt*
* after concentration
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 6
Hall C in Kamioka: XMASS
Hall C: 15m,21m,15m (h,d,w)
water in tank:10m high
10m Ø
outer detector bigenough for final20 ton detector
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 7
XMASS from the Outside In:
outer detector (OD):72 x 20inch PMTs
Hamamatsu R3600
calibrationport
inner detector (ID):642 x 2 inch PMTs
Hamamatsu R10789-11LXe: 1100 kg
(total) 835 kg
(inside PMTs)
100 kg(fiducial)
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 8
Inner Detector Structure:2nd
LAYER
FILLER
LXe in detector:1100kg
in sensitive volume:835kg
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 9
Electronics:
new: FADCs
CAEN V17518 ch/board
bandwidth 500MHz,sampling rate 1GS/s
resolution 10bit1.2 μs window
so far: Super-Kamiokande ATMs
12 bit ADC/TDCintegration: -100ns – +300ns
1.2 μs window
both systems will run in parallel ← signal is split
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 10
XMASS Calibration System:“internal” γ calibration for XMASS:
- 57Co (122keV) ← anchor of energy scale
- 241Am (59.5keV), 109Cd (88keV), 55Fe (5.9keV)
“external” (hose)- 60Co, 137Cs- 252Cf neutrons (need FADC)
(different sources → slightly different shapes [materials...])
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 11
Low BG PMT Development:
Hamamatsu R10789: QE 28-39%+
XMASS photocathode coverage: 62.4%⇓
light yield: 14.7 PE/keV @ 122 keV
BG: biggest worry → PMTspecial development; incl. base:U-chain 0.70±0.28mBq/PMTTh-chain 1.5±0.31 mBq/PMT40K < 5.1 mBq/PMT60Co 2.9±0.16 mBq/PMT
… but:total BG larger than expectedyet comparable to other experiments,like CRESST, CDMS, or CoGeNT
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 12
What Did We Learn?surface contamination: β-decays...main culprits:- PMT aluminum seal: 210Pb, 238U chain- Cu surface: 210Pb (222Rn exposure...)
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 13
XMASS Refurbishmentcountermeasures:
- surface cleanup ← Cu electropolished: “rm -r U* Th*”
- remove Gore-Tex (presumed guilty until proven innocent … )
- cover PMT aluminum seal:- vapor deposition of Al on side of window- Cu ring around aluminum seal- electropolished Cu cover above Cu rings
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 14
Radon & Dust: Defense in Depth(pictures from 2010 detector assembly:)
this time:
hall C → now clean room (class 1000)
→ three levels of clean roomto tent in water tank
→ much improved clean roomconditions at assembly site
also improved: - radon free air availability and flow- PMT holder will be kept in special encasing during
assembly→ expect better than one order of magnitude reduction in background !!!
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 15
On the Way to XMASS 2: XMASS 1.5- still a DM detector- inner Ø: 1.5 m- contains 5 tons of LXe- fiducial mass 1 ton~ 1800 PMTs (or move to 3 inch ?)
lessons from XMASS 800kg:new PMTs!
w/dome-shaped photocathode← see nearby surface !!!
want to startin 2014 !!
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 16
New PMT for XMASS 1.5actively being developed w/Hamamatsu:
dome shaped photocathodeto detect light entering from the side:i.e. from the surrounding surfaces...
→ effectiveness verified by MC
(photos show prototype; no final design yet)
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 17
Conclusions- there is a well developed and active Dark Matter program at Kamioka
- our self-shielding, single phase LXe detector technology is:← producing results← readily scalable← delivering high light yield → low threshold
- initial contamination problems are understood and being addressed:← the fundamental technology is debugged and proven !
- XMASS 800kg data taking will resume in September 2013:← stay tuned !!
- XMASS 1.5 will start in 2014:← look forward !!!
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 18
Backup
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 19
57Co Calibration: reconstruction:data MC
@ center:data vs. MC
W (59.3 keV)
57C
o (1
22 k
eV)
57C
o (1
36 k
eV)
center position setsenergy scale:
→ 14.7 p.e./keVee
resolution 4% rms
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 20
Xe Distillation: (85)Kr Removal
K.Abe et al, Astroparticle Physics
31(2009), p290
capacity of XMASS Xe distillation system:6kg/h; did 1 ton in ~ 1 week → (3.3±1.1)ppt
otherwise:extensive materials validationbefore construction:
IPMU Lab:U, Th → HP-Ge ← few 100ppt
→ ICP-MS ← 1ppq*Kr → API-MS ← 1ppt** after concentration
hall C distillation system:(used before filling detector)
experience:detector stable w/o:- routine getter operation- active Rn removal
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 21
Decay Chains:
from: http://radiokimia.blogspot.com.br/2011/04/u-235-u-238-and-th-232-decays-series.html
July 6, 2013 Kai Martens @ ICRC 2013 for XMASS 22
Background Comparisons:
XMASS 800kg full volume
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